Conventional non-pneumatic solid rubber tires have been used prior to pneumatic tires. As vehicle speeds increased and ride characteristics became more important, the need for a pneumatic structure emerged. The pneumatic tire provided a solution to the problems and limitations of solid, non-pneumatic tires.
The conventional pneumatic tire is an efficient structure that has endured as a solution to conventional vehicle requirements. The conventional pneumatic tire is a “tensile structure.” Tensile structures contain a compression structure for providing a tensile preload in the tensile structure. The tensile structure may typically accept no compression, and the compression structure, no tension. In pneumatic tires, cords are the tensile structure and compressed air is the compression structure.
A drawback of a conventional pneumatic tire is that it is pneumatic. Air contained under pressure may, and typically does, escape at inopportune times, at least from a vehicle operator's view point.
A non-pneumatic tire has no air under pressure. It is a tire structure that performs similarly to a pneumatic tire, without requiring air contained under pressure. Communication of a non-pneumatic tire with a road/contact surface in the area of the tire footprint, or contact patch, provides the only force input to the vehicle from the contact surface and provides the handling forces and load to the contact surface. Thus, a non-pneumatic tire has these fundamental characteristics in common with a pneumatic tire.
A conventional pneumatic tire has unique flexure and load carrying characteristics. Shock and deflections, although occurring locally in the area radially inwardly of the footprint, may be absorbed globally by the entire tire structure. Cornering characteristics are achieved by a combination of increases and decreases in tension of the tire sidewall.
A conventional non-pneumatic tire must similarly be able to withstand shock loads and dissipate absorbed energy. However, unlike a pneumatic tire, a non-pneumatic tire typically absorbs shocks and deflects locally within the footprint or contact patch. Such localized deflection of a non-pneumatic tire must therefore also exhibit high dampening characteristics.
Further, any tire in a running condition must be able to dissipate heat. The nature of dampening loads is a form of energy dissipation. Energy absorbed is converted to heat. Heat, in turn, may affect tire performance and may result in premature tire failure. Thus, efficient dissipation of heat is essential for any tire. Ideally, energy is only absorbed by the tire in the area radially inward of the footprint or contact patch so that energy may be removed from such area during the remainder of the tire's revolution.
However, rubber is a poor conductor of heat. The thicker the rubber, the greater the heat accumulation. The heat accumulation may be mitigated to a controlled level by having thin material cross sections with high air circulation.
Urethane tires can operate at temperatures as high as about 93° C. (200° F.). Temperatures higher than 121° C. (250° F.) degrees for prolonged periods will cause a weakening of the urethane. If the temperature of a urethane tire rises high enough, premature failure of the urethane tire may occur.
One conventional non-pneumatic tire/wheel includes a central portion of resilient material, an outer resilient tread portion, and an interposed shock absorbing portion comprising a plurality of crossed webs of resilient material formed with the center and tread portions. Formed in the inner portion of the shock absorbing portion is an annular series of orifices. The orifices are set transversely and slightly overlapping. Each orifice extends across the entire axial width of the shock absorbing portion. A pair of disks is also provided with similar orifices. One disk is positioned on each side of the tire/wheel with orifices aligned with those of the shock absorbing portion. Upon molding, one integral unit is formed. This cushion tire/wheel eliminated the metal parts used to fasten a pneumatic or solid rubber tire to a wheel.
Such conventional attempts to develop a non-pneumatic tire failed to provide adequate heat dissipation along with adequate load bearing capability. As vehicle speeds have increased, these concepts have been incapable of meeting the needs of the passenger and truck tires.
Another conventional non-pneumatic tire is integrally molded from an elastomeric material to form a unitary structure comprising inner and outer “hoops.” The outer hoop is supported and cushioned by a plurality of circumferentially spaced apart planar ribs and a planar central web, which connects the hoops at their circumferential center. The web lies in a plane perpendicular to the rotational axis of the tire. The ribs extend axially along the inner and outer hoops connecting the hoops with edges of the ribs along opposite faces of the web. The planar ribs may be undercut at the radial extremes to assure bending and no buckling unless a critical load is exceeded.
Another conventional non-pneumatic tire has an equatorial plane, an axis perpendicular to the equatorial plane, an annular tread rotatable about the axis, and an annular elastomer body made from a material having a Shore A hardness in the range of 60 to 100. The elastomer body has first and second spaced lateral sides. The sides are spaced equidistant from the equatorial plane and extend between the tread and the rim. The body has openings positioned equidistant from the axis, some of which extend from the first side and others which extend from the second side to form first and second sets of openings. The sets of openings extend from respective sides toward the equatorial plane. The openings form equally spaced columns of elastomer material in the body. The columns formed by the first set of openings are inclined to the radial direction of the tire, and the columns formed by the second set of openings are generally inclined to the radial direction of the tire, but are opposite in inclination with respect to the columns formed by the first set of openings.
The National Aeronautics and Space Administration (NASA) has developed surface vehicles to support long range lunar exploration and the development of a lunar outpost. These vehicles are heavier and travel greater distances than the Lunar Roving Vehicle (LRV) developed for the Apollo program in the late 1960s. Consequently, new tires will be required to support up to ten times the weight, and last for up to one hundred times the travel distance, as compared to those used on the Apollo LRV, thereby requiring operational characteristics similar to passenger vehicles used on earth. However, conventional rubber pneumatic tires cannot function acceptably in space.
For example, rubber properties vary significantly between the cold temperatures experienced in shadow (down to 40 K) and the hot temperatures in sunlight (up to 400 K). Further, rubber degrades when exposed to direct solar radiation, without atmospheric protection. Finally, an air-filled tire is not permissible for manned lunar vehicles because of the possibility of a flat tire. To overcome these limitations, a tire design has been developed for the Apollo LRV and was successfully used on Apollo missions 15, 16, and 17. This non-pneumatic tire was woven from music wire, which was robust to lunar temperature variations and solar radiation, operated in vacuum, and did not require air for load support. This structure further functioned to contour to the lunar terrain, which facilitated traction and reduced vibration transfer to the Apollo LRV.
As stated above, because of the new weight and distance requirements for lunar vehicles, a tire with greater strength and durability was required. One conventional wheel and non-pneumatic tire assembly has a variable diameter which, in addition to changing its diameter, may also change its width, thereby increasing the area of the wheel that engages the ground. Thus, this non-pneumatic tire may be adjusted to increase a vehicle's performance according to the terrain over which it is traveling. This tire/wheel has arching members with first and second ends connecting a wheel hub. The arching members extend outwardly in an arc between the first and second ends. The arching members form a plurality of flexible hoops spaced circumferentially around the hub and extending radially outward from the hub.
More specifically, this conventional non-pneumatic tire/wheel forms a cage composed of thirty-eight equally spaced radially extending hoops that arch between axially outer rims of a hub. The hoops are made of helical steel springs filled by wires cut to a desired length and threaded through the center of the springs. The conventional hub may be expanded/contracted axially for varying the diameter of the tire/wheel.
The wire mesh design of the Apollo LRV tire was found to not be readily scalable. Specifically, the increase in wire diameter to create a tire that supported ten times the load of the original design created two significant limitations: 1) the ability to contour to the terrain was lost, thus limiting traction and ability to isolate vibration; and 2) the increased wire stresses limited functional life.
Thus, another conventional non-pneumatic tire/wheel includes a plurality of helical springs. Each helical spring includes a first end portion, a second end portion, and an arching middle portion interconnecting the first end portion and the second end portion. Each helical spring is interwoven, or interlaced, with at least one other helical spring of the plurality thereby forming a woven toroidal structure extending about an entire circumference of the non-pneumatic tire/wheel. A subset of helical springs may be secured to a first annular rim of a wheel and/or a second annular rim of the wheel. A wheel with an annular rim at each axial side of the tire may secure the tire to the wheel. Thus, as compared to structures of conventional pneumatic tires, the woven/laced toroidal structure of interwoven helical springs defines a first ply for the non-pneumatic tire. A second ply may radially overlap the first ply. Such a second ply may comprise the same interwoven toroidal structure as the first ply.
As a result, an improved non-pneumatic tire for use in specific applications is desirable.
Definitions
“Apex” means an elastomeric filler located radially above the bead core and between the plies and the turnup ply.
“Annular” means formed like a ring.
“Aspect ratio” means the ratio of its section height to its section width.
“Axial” and “axially” are used herein to refer to lines or directions that are parallel to the axis of rotation of the tire.
“Bead” means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim.
“Belt structure” means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having cords inclined respect to the equatorial plane of the tire. The belt structure may also include plies of parallel cords inclined at relatively low angles, acting as restricting layers.
“Bias tire” (cross ply) means a tire in which the reinforcing cords in the carcass ply extend diagonally across the tire from bead to bead at about a 25°-65° angle with respect to equatorial plane of the tire. If multiple plies are present, the ply cords run at opposite angles in alternating layers.
“Breakers” means at least two annular layers or plies of parallel reinforcement cords having the same angle with reference to the equatorial plane of the tire as the parallel reinforcing cords in carcass plies. Breakers are usually associated with bias tires.
“Cable” means a cord formed by twisting together two or more plied yarns.
“Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
“Casing” means the carcass, belt structure, beads, sidewalls and all other components of the tire excepting the tread and undertread, i.e., the whole tire.\
“Chipper” refers to a narrow band of fabric or steel cords located in the bead area whose function is to reinforce the bead area and stabilize the radially inwardmost part of the sidewall.
“Circumferential” means lines or directions extending along the perimeter of the surface of the annular tire parallel to the Equatorial Plane (EP) and perpendicular to the axial direction; it can also refer to the direction of the sets of adjacent circular curves whose radii define the axial curvature of the tread, as viewed in cross section.
“Cord” means one of the reinforcement strands of which the reinforcement structures of the tire are comprised.
“Cord angle” means the acute angle, left or right in a plan view of the tire, formed by a cord with respect to the equatorial plane. The “cord angle” is measured in a cured but uninflated tire.
“Denier” means the weight in grams per 9000 meters (unit for expressing linear density). Dtex means the weight in grams per 10,000 meters.
“Elastomer” means a resilient material capable of recovering size and shape after deformation.
“Equatorial plane (EP)” means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread; or the plane containing the circumferential centerline of the tread.
“Fabric” means a network of essentially unidirectionally extending cords, which may be twisted, and which in turn are composed of a plurality of a multiplicity of filaments (which may also be twisted) of a high modulus material.
“Fiber” is a unit of matter, either natural or man-made that forms the basic element of filaments. Characterized by having a length at least 100 times its diameter or width.
“Filament count” means the number of filaments that make up a yarn. Example: 1000 denier polyester has approximately 190 filaments.
“Flipper” refers to a reinforcing fabric around the bead wire for strength and to tie the bead wire in the tire body.
“Footprint” means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load.
“Gauge” refers generally to a measurement, and specifically to a thickness measurement.
“Harshness” means the amount of disturbance transmitted by a tire when it passes over minor, but continuous, road irregularities.
“High Tensile Steel (HT)” means a carbon steel with a tensile strength of at least 3400 MPa @ 0.20 mm filament diameter.
“Hysteresis” means a retardation of the effect when forces acting upon a body are changed.
“Inner” means toward the inside of the tire and “outer” means toward its exterior.
“Innerliner” means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire.
“LASE” is load at specified elongation.
“Lateral” means an axial direction.
“Lay length” means the distance at which a twisted filament or strand travels to make a 360 degree rotation about another filament or strand.
“Mega Tensile Steel (MT)” means a carbon steel with a tensile strength of at least 4500 MPa @ 0.20 mm filament diameter.
“Normal Load” means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
“Normal Tensile Steel (NT)” means a carbon steel with a tensile strength of at least 2800 MPa @ 0.20 mm filament diameter.
“Ply” means a cord-reinforced layer of rubber-coated radially deployed or otherwise parallel cords.
“Pneumatic tire” means a laminated mechanical device of generally toroidal shape (usually an open-torus) having beads and a tread and made of rubber, chemicals, fabric, steel, and/or other materials. When mounted on the wheel of a vehicle, the pneumatic tire, through its tread, provides traction and contains a fluid that sustains the vehicle load.
“Radial” and “radially” are used to mean directions radially toward or away from the axis of rotation of the tire.
“Radial Ply Structure” means the one or more carcass plies or which at least one ply has reinforcing cords oriented at an angle of between 65° and 90° with respect to the equatorial plane of the tire.
“Radial Ply Tire” means a belted or circumferentially-restricted pneumatic tire in which at least one ply has cords which extend from bead to bead are laid at cord angles between 65° and 90° with respect to the equatorial plane of the tire.
“Rim” means a support for a tire or a tire and tube assembly upon which the tire is secured.
“Section Height” means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.
“Section Width” means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.
“Sidewall” means that portion of a tire between the tread and the bead.
“Spring rate” means the stiffness of a tire or spring expressed as the slope of a load defection curve.
“Super Tensile Steel (ST)” means a carbon steel with a tensile strength of at least 3650 MPa @ 0.20 mm filament diameter.
“Tenacity” is stress expressed as force per unit linear density of the unstrained specimen (gm/tex or gm/denier). Used in textiles.
“Tensile” is stress expressed in forces/cross-sectional area. Strength in psi=12,800 times specific gravity times tenacity in grams per denier.
“Toe guard” refers to the circumferentially deployed elastomeric rim-contacting portion of the tire axially inward of each bead.
“Tread” means a molded rubber component which, when bonded to a tire casing, includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load.
“Tread width” means the arc length of the tread surface in a plane including the axis of rotation of the tire.
“Turnup end” means the portion of a carcass ply that turns upward (i.e., radially outward) from the beads about which the ply is wrapped.
“Ultra Tensile Steel (UT)” means a carbon steel with a tensile strength of at least 4000 MPa @ 0.20 mm filament diameter.
“Yarn” is a generic term for a continuous strand of textile fibers or filaments. Yarn occurs in the following forms: 1) a number of fibers twisted together; 2) a number of filaments laid together without twist; 3) a number of filaments laid together with a degree of twist; 4) a single filament with or without twist (monofilament); 5) a narrow strip of material with or without twist.